The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment the present invention is related to encapsulated toner compositions comprised of a core containing a fluorocarbon-incorporated resin binder, that is for example a copolymer of a fluorocarbon and a monomer subsequent to polymerization, and colorants with a polymeric shell thereover preferably prepared by interfacial polymerization. Another specific embodiment of the present invention relates to encapsulated toner compositions comprised of a core containing a fluorocarbon-incorporated polymer resin such as those derived from the copolymerization of a suitably functionalized fluorocarbon compound with an addition-type monomer, and dye or pigment particles, which core is encapsulated by a polymeric coating such as a polyurea, a polyurethane, a polyamide, a polyester, or mixtures thereof. Examples of advantages associated with the toner compositions of the present invention include the elimination and/or the minimization of image ghosting, excellent fixing characteristics, acceptable release properties enabling selection of the toners, for example, in imaging systems wherein a release fluid such as a silicone oil can be avoided, substantially no toner agglomeration, acceptable powder flow characteristics, and avoidance or minimization of core binder adherence to imaging components such as, for example, photoreceptors and dielectric receivers. The toner compositions of the present invention can be selected for a variety of known imaging processes including electrophotographic and ionographic processes. Preferably, the toner compositions are selected for pressure fixing processes in ionographic printing devices wherein dielectric receivers such as silicon carbide are utilized, reference U.S. Pat. No. 4,885,220 entitled Amorphous Silicon Carbide Electroreceptors, the disclosure of which is totally incorporated herein by reference. The toner compositions of the present invention can be selected for commercial ionographic printers such as the Delphax S9000 S6000, S4500, S3000, Xerox 4075.TM. wherein, for example, transfixing is utilized, that is fixing of the developed image is accomplished by simultaneously transferring and fixing the developed images with pressure. In another specific embodiment of the present invention the toners possess high fixing characteristics enabling their selection for duplex imaging processes. Moreover, in other embodiments of the present invention the toners thereof possess acceptable powder flow and surface release properties, thus enabling efficient transfer of toned images to paper substrate, and eliminating or substantially suppressing image ghosting problems. The desirable surface release properties of the toner compositions of the present invention also enable their use in pressure fixing and thermal energy fusing processes without the use of a release agent, such as a silicone oil, to prevent image offset to the pressure or fuser rolls.
The toner compositions of the present invention can in one specific embodiment, be prepared by the interfacial polymerization of shell-forming monomers, followed by in situ free-radical polymerization of core binder-forming monomers. Thus, in one embodiment the present invention is directed to a process for the simple, and economical preparation of pressure fixable encapsulated toner compositions by interfacial/free-radical polymerization methods wherein there are selected as core monomers an addition-type monomer or monomers, and an addition-polymerizable fluorocarbon compound. Other process embodiments of the present invention relate to, for example, interfacial/free-radical polymerization processes for obtaining encapsulated colored toner compositions. Further, in another process aspect of the present invention the encapsulated toners can be prepared without organic solvents thus eliminating explosion hazards associated therewith; and therefore, these processes do not require expensive and hazardous solvent separation and recovery steps. Moreover, with the aforementioned process of the present invention there is obtained in some instances improved throughput yield per unit volume of reactor size since, for example, the extraneous solvent component can be replaced by liquid core monomer(s) which would serve as a diluting vehicle and as a reaction medium. The aforementioned toners prepared in accordance with the process of the present invention are useful for permitting the development of images in reprographic imaging systems, inclusive of electrophotographic and ionographic processes wherein pressure fixing, especially pressure fixing in the absence of heat, is selected.
Encapsulated and cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy since the toner compositions used can be fixed at room temperature. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fixed under high pressure, which has a tendency to severely disrupt the toner's fixing characteristics. This can result in images of low resolution, or no images whatsoever. The high fixing pressure can also lead to objectionable paper calendering and glossy images. With some of the prior art cold pressure toner compositions, substantial image smearing can result from the high pressures used. Additionally, the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions generate images of inferior crease and rub resistance properties, and the said images can often be readily rubbed off with pressure or removed by folding. Furthermore, many of the prior art toner compositions are prepared by processes which employ organic solvents as diluting vehicles and as reaction media, and these may create explosion hazards; and further these processes will be costly because they require the additional solvent separation and recovery steps. Furthermore, with many of the prior art processes narrow size dispersity particles cannot easily be achieved by conventional bulk homogenization techniques as contrasted with the process of the present invention wherein narrow size dispersity particles are easily obtained. In addition, many prior art processes provide deleterious effects on toner particle morphology and bulk density as a result of the removal of solvent and the subsequent collapse or shrinkage of toner particles during particle isolation resulting in a toner of very low bulk density, which disadvantages are substantially eliminated with the process of the present invention. More specifically, thus with the encapsulated toners of the present invention control of the properties of both the core and shell materials can be achieved. Specifically, with the encapsulated toners of the present invention image ghosting is eliminated in many instances primarily because of the chemical reaction presence of certain fluorocarbon moieties in the core binder structure illustrated herein. Image ghosting is one of the undesirable print quality problems encountered in ionographic printing processes. It refers to the repetitious printing of unwarranted images, and is related to the contamination of the dielectric receiver surface by some unremoved residual toner materials. The toner compositions of the present invention effectively prevent the aforementioned contamination by imparting desirable and acceptable surface release properties to toners, thus enabling efficient transfer of developed images and efficient cleaning of dielectric receiver surface.
In a patentability search report, the following prior art U.S. Pat. Nos. were recited: 4,339,518, which relates to a process of electrostatic printing with fluorinated polymer toner additives where suitable materials for the dielectric toner are thermo plastic silicone resins and fluorine containing resins having low surface energy, reference column 4, beginning at line 10, note for example the disclosure in column 4, line 16, through column 6; 4,016,099, which discloses methods of forming encapsulated toner particles and wherein there is selected organic polymers including homopolymers and copolymers such as vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, and the like, see column 6, beginning at line 3, wherein there can be selected as the core materials polyolefins, polytetrafluoroethylene, polyethylene oxide and the like, see column 3, beginning at around line 18; 4,265,994 directed to pressure fixable capsule toners with polyolefins, such as polytetrafluoroethylene, see for example column 3, beginning at line 15; 4,497,885, which discloses a pressure fixable microcapsule toner comprising a pressure fixable component, a magnetic material, and other optional components, and wherein the core material can contain a soft material typical examples of which include polyvinylidenefluoride, polybutadiene, and the like, see column 3, beginning at line 10; 4,520,091 discloses an encapsulated toner with a core which comprises a colorant, a dissolving solvent, a nondissolving liquid and a polymer, and may include additives such as fluorine containing resin, see column 10, beginning at line 27; 4,590,142 relating to capsule toners wherein additives such as polytetrafluoroethylenes are selected as lubricating components, see column 5, beginning at line 52; 4,599,289 and 4,803,144.
With further specific reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there is disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there are disclosed in the prior art encapsulated toner compositions containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676 (now abandoned), the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.
Liquid developer compositions are also known, reference for example U.S. Pat. No. 3,806,354, the disclosure of which is totally incorporated herein by reference. This patent illustrates liquid inks comprised of one or more liquid vehicles, colorants such as pigments, and dyes, dispersants, and viscosity control additives. Examples of vehicles disclosed in the aforementioned patent are mineral oils, mineral spirits, and kerosene; while examples of colorants include carbon black, oil red, and oil blue. Dispersants described in this patent include materials such as polyvinyl pyrrolidone. Additionally, there are described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically, or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
Accordingly, there is a need for encapsulated toner compositions with many of the advantages illustrated herein. More specifically, there is a need for encapsulated toners wherein image ghosting is eliminated or minimized. Also, there is a need for encapsulated toners which provide high image fix levels, and which compositions enable, for example, their selection for use in duplex imaging processes. Moreover, there is a need for encapsulated toners, including colored toners wherein image ghosting, toner offsetting, and the like are avoided or minimized. Additionally, there is a need for encapsulated toners, including colored toners with excellent release characteristics enabling their selection in imaging systems without having to use surface release fluids such as silicone oils to prevent image offsetting to the fixing or fusing roll. Furthermore, there is a need for encapsulated toners, including colored toners with substantially no toner agglomeration, and extended shelf life exceeding, for example, one to two years. Also, there is a need for encapsulated toners that have been surface treated with additives such as carbon blacks, graphite or the like to impart to their surfaces certain conductivity characteristics such as a volume resistivity of from about 1.times.10.sup.3 ohm-cm to about 1.times.10.sup.8 ohm-cm. Conductive toners enable the desirable single component inductive development processes currently selected for many ionographic printers. Furthermore, there is a need for encapsulated toners wherein surface additives, such as metal salts or metal salts of fatty acids and the like, are utilized to assist in the release of the toned images from the imaging component such as a photoreceptor or a dielectric receiver to paper substrate. There is also a need for simple, economical processes for the preparation of encapsulated toners. Specifically, there is a need for interfacial/free-radical polymerization processes for black and colored encapsulated toner compositions, wherein the core contains colorants, and a fluorocarbon-incorporated core binder derived from two core monomers or precursors, one of which is an addition-polymerizable fluorocarbon compound. Another need resides in the provision of a simple economical process wherein in some embodiments organic solvents are not employed as the diluting vehicles or as reaction media. Furthermore, there is a need for improved processes that will enable pressure fixable toner compositions with pressure-rupturable hard shells, pressure-fixable soft cores, and wherein the properties of the toner's constituent materials such as the core binder molecular weight and molecular weight dispersity can be desirably controlled. Moreover, there is a need for enhanced flexibility in the design and selection of materials comprising the core and shell of toner particles, and the control of the physical properties, such as bulk density, particle size, and size dispersity of the toner.